1. Field of the Invention
The present invention relates to a method of manufacturing a cylindrical capacitor having a cylindrical ceramic body serving as a dielectric member, and more particularly, it relates to an improvement in a method of forming an inner electrode provided on the inner peripheral surface of the cylindrical ceramic body.
2. Description of the Prior Art
In general, a cylindrical capacitor is provided with a cylindrical ceramic body in order to attain a prescribed capacitance through an inner electrode and an outer electrode which are provided on inner and outer peripheral surfaces of the ceramic body respectively in an opposite manner. Various types of such cylindrical capacitors are provided by various methods of forming the inner and outer electrodes, configurations of the ceramic bodies and the like FIGS. 9, 16, 26 and 28 are illustrative of four typical cylindrical capacitors obtained through various embodiments of the present invention. With reference to these figures, the structure of the cylindrical capacitors and a conventional method of manufacturing the same will now be described.
A cylindrical capacitor 1 as shown in FIG. 9 is provided with a cylindrical ceramic body 2, an inner electrode 3 and an outer electrode 4. The ceramic body 2 has oppositely provided first and second end surfaces 5 and 6. It also has inner and outer peripheral surfaces 7 and 8 extending between the first and second end surfaces 5 and 6 which are opposite to each other. The ceramic body 2 further has an opening 10 which communicates with an inner space 9 enclosed by the inner peripheral surface 7 only at the first end surface 5
The inner electrode 3 is formed to extend from the inner peripheral surface 7 of the ceramic body 2 to a part of the outer peripheral surface 8, across through the first end surface 5, for electrical connection with the exterior, thereby to define a terminal electrode part 11 on the outer peripheral surface 8.
The outer electrode 4 is formed on the outer peripheral surface 8 of the ceramic body 2 to be opposite to the inner electrode 3, separated by the ceramic body 2. This outer electrode 4 is adapted to extend onto the second end surface 6 of the ceramic body 2.
A cylindrical capacitor 1a as shown in FIG. 16 has many elements which are substantially identical in structure to the cylindrical capacitor 1 as shown in FIG. 9. Therefore, corresponding components are indicated by the same reference numerals to avoid redundant description.
The cylindrical capacitor 1a as shown in FIG. 16 is different from the cylindrical capacitor 1 in FIG. 9 in that the inner electrode 3a thereof extends all the way to a bottom surface 12 of an inner space 9 of a ceramic body 2 and covers the same.
A cylindrical capacitor 1b as shown in FIG. 26 is different from the foregoing capacitors in that the configuration of a ceramic body 2b is different from the respective ceramic bodies in the cylindrical capacitors 1 and 1a as shown in FIGS. 9 and 16. The ceramic body 2b is provided with a first opening 10b which communicates with an inner space 9b at a first end surface 5b, as well as a second opening 13 which communicates with the inner space 9b at a second end surface 6b.
An inner electrode 3b extends from an inner peripheral surface 7b of the ceramic body 2b to an outer peripheral surface 8b across the first end surface 5b, to form a terminal electrode part 11b on the outer peripheral surface 8b.
On the other hand, an outer electrode 4b extends from the outer peripheral surface 8b of the ceramic body 2b to the second end surface 6b.
A cylindrical capacitor 1c as shown in FIG. 28 has several elements which are substantially identical in structure to the cylindrical capacitor 1b as shown in FIG. 26. Therefore, components corresponding to those of FIG. 26 are indicated by the same reference numerals, to avoid redundant description.
The cylindrical capacitor 1c as shown in FIG. 28 is different from the cylindrical capacitor 1b of FIG. 26 in that the outer electrode 4c is formed not to extend over a second end surface 6b of a ceramic body 2b.
Generally, in order to form the inner electrode 3, 3a or 3b and the outer electrode 4, 4b or 4c of the aforementioned cylindrical capacitor 1, 1a, 1b, or 1c, metal paste containing metal such as silver or silver-palladium for forming these electrodes is coated to form metal paste films, which are then subjected to baking. In such a method, the step of coating the metal paste on the outer surface of the capacitor can be relatively easily performed by utilizing a transfer roller, a brush or a knife with respect to the terminal electrode part 11 or 11b of the inner electrode 3, 3a or 3b, and the outer electrode 4, 4b or 4c, which are provided on the outwardly directed surface of the ceramic body 2 or 2b or parts thereof. However, it is rather difficult to form a metal paste film for providing a part of the inner electrode 3, 3a or 3b positioned on the inner peripheral surface 7 or 7b.
In general, such a metal paste film for providing the part of the inner electrode 3, 3a or 3b to be positioned on the inner peripheral surface 7 or 7b has been formed by inserting a rotating pin with metal paste applied thereon, into the inner space 9 or 9b of the ceramic body 2 or 2b.
However, such a method of coating metal paste through a rotating pin has the following disadvantages: (1) It is difficult to form a metal paste film of uniform thickness on the inner peripheral surface of a ceramic body.
(2) In the inner electrode 3 or 3b as shown in FIG. 9, 26 or 28 whose edge is located on the inner peripheral surface 7 or 7b, the edge may be provided in a corrugated state. Further, it is difficult to always provide such an edge in a constant position in the axial direction of the ceramic body. Thus, the surface areas of such inner electrodes may vary from product to product.
(3) In case of the inner electrode 3a as shown in FIG. 16 which extends toward and across the bottom surface 12 of the ceramic body 2, it is difficult to coat the metal paste by means of a rotating pin, particularly at the internal angles at which the inner peripheral surface 7 and the bottom surface 12 intersect with each other. Thus, a part of a metal paste film formed on the bottom surface 12 may be isolated from that formed on the inner peripheral surface 7.
(4) When the ceramic body is changed in inner diameter, the rotating pin must be replaced by another pin having a corresponding outer diameter, whereby it takes time for the replacement and following adjustment of the position for mounting the rotating pin, and this increases the required manufacturing time.
(5) It is extremely difficult to coat metal paste on the inner peripheral surfaces of a large number of ceramic bodies at the same time by means of rotating pins, and hence high productivity cannot be expected.
(6) Metal paste cannot be applied by a rotating pin to a ceramic body having an inner peripheral surface having a non-circular cross-sectional configuration but rather having, e.g., a rectangular cross-sectional configuration.